Two-way magnetorheological fluid valve assembly and devices utilizing same

ABSTRACT

A controllable valve assembly (18) applicable in Magnetorheological (MR) fluid devices (20), such as MR mounts and MR dampers. The valve assembly (18) includes a valve body (32) having a magnetic circuit (40) contained therein which carries magnetic flux φ, a controllable passageway (42) within the magnetic circuit (40), a MR (magnetically controlled) fluid (44) including soft-magnetic particles in a liquid carrier contained in the controllable passageway (42), a magnetic flux generator, such as a wound wire coil (46), generating magnetic flux φ which is directed through the MR fluid (44) in the controllable passageway (42) thereby generating &#34;rheology&#34; changes causing restriction in flow of MR fluid (44) therethrough. In one aspect, a one-way check valve (34) is operative with a passive passageway (36) which is arranged in parallel relationship to the controllable passageway (42) provides &#34;asymmetric&#34; damping across the controllable valve (18) creating higher pressure differentials in a first direction and a lower in a second direction without &#34;rapidly switching&#34; the current to the coil (46). In another aspect, &#34;asymmetric&#34; damping is provided by a &#34;changeable gap&#34; formed by a moveable wall portion of the controllable passageway (42). In a third aspect, a first controllable passageway provides controllable flow in a first direction and a second controllable passageway provides controllable flow in a second direction, thereby provide &#34;asymmetry.&#34; In a fourth aspect, &#34;asymmetry&#34; is provides by a &#34;variable magnetic short&#34; which changes magnetic circuit reluctance dependent on flow direction.

This application is a divisional of pending U.S. patent application Ser.No. 08/811,896, filed Mar. 5, 1997.

FIELD OF THE INVENTION

This invention relates to the area of controllable fluid valves anddevices. Specifically, it relates to controllable fluid valves anddevices which utilize a magnetorheological (magnetically controllable)fluid therein.

BACKGROUND OF THE INVENTION

Dampers and mounts are known which use a hydraulic fluid as the workingmedium to create damping forces/torques and to control motion, shock,and/or vibration. One special class of these devices are controllable.In particular, controllable mounts and dampers are known which includeElectrorheological fluid (ER), Electrophoretic fluid (EP),Magnetorheological fluid (MR), and Hydraulic fluid (Semi-active), etc.Examples of ER-type mounts and dampers may be found in U.S. Pat. No.4,733,758 to Duclos et al. and U.S. Pat. No. 5,029,677 to Mitsui.Further discussions of ER devices may be found in SAE 881134 entitled"Design of Devices Using Electrorheological Fluids" by T. Duclos.Descriptions of EP-type dampers may be found in U.S. Pat. No. 5,018,606to J. D. Carlson. Examples of Semi-Active hydraulic dampers and valvesmay be found in U.S. Pat. No. 3,807,678 to Karnopp et al. and U.S. Pat.No. 5,207,774 to Wolfe et al.

Of particular interest are Magnetorheological (MR) fluid devices(hereinafter MR devices), as they only require small electrical currents(typically several amps or less) and do not present the potential shockhazard that ER devices do, because they operate on much lower voltage(typically 12 volts or less). MR devices employ a controllableMagnetorheological (MR) fluid comprised of small soft-magnetic particlesdispersed within a liquid carrier. Typical particles include carbonyliron, or the like, having various shapes, but which are preferablyspherical, and which exhibit mean dimensions of between about 0.1 μm to500 μm, and more preferably between about 1 μm and 100 μm. The carrierfluids include various known hydraulic oils, and the like. These MRfluids exhibit a thickening behavior (a rheology change), sometimesreferred to as an "apparent viscosity change", upon being exposed to amagnetic field of sufficient strength. The higher the magnetic fieldstrength to which the MR fluid is exposed, the higher the differentialpressure (flow restriction or damping force) that can be achieved withinthe particular MR device (ex. MR damper, MR mounting).

Examples of prior art fluids can be found in WO 94/10694, WO 94/10693,and WO 94/10692, the inventions of which are commonly assigned to theassignee of the present invention. In particular, MR fluid devicesprovide ease of controllability through simple user selectedfluctuations in the electrical current supplied to the magnetic fieldgenerator (generally a wound-wire coil) in the device. Notably, MRfluids and devices have demonstrated durability yet unobtained with ERdevices (which exhibit a change in rheology upon being exposed to"electric" fields). Further, MR devices provide simplicity previouslyunachieved with controllable Semi-active devices, in that thecontrollable valves have few or no moving parts.

Descriptions of prior art MR devices can be found in U.S. applicationSer. No. 08/304,005 entitled "Magnetorheological Fluid Devices andProcess of Controlling Force in Exercise Equipment Utilizing Same", U.S.Ser. No. 08/613,704 entitled "Portable Controllable Fluid RehabilitationDevices", U.S. Ser. No. 08/674,371 entitled "Controllable Brake", U.S.Ser. No. 08/674,179 entitled "Controllable Vibration Apparatus" and U.S.Pat. Nos. 5,547,049, 5,492,312, 5,398,917, 5,284,330, and 5,277,281, allof which are commonly assigned to the assignee of the present invention.Notably, these MR devices provide user-variable/selectable controlforces or torques and describe such devices as MR mounts, MR dampers,and MR brakes.

Notably, the MR fluid valves (hereinafter MR valve) described in theprior art devices such as MR dampers, MR mounts, and the like, lack theability to tune the output characteristics of the device/apparatuswithout some "rapid" control thereof. In other words, they require"rapidly switching" electronics in order to provide "asymmetric" dampingin the various directions. For example, different dampingcharacteristics in compression and extension are achieved in the priorart by applying one current in the compression direction and thenrapidly switching to a second current in extension.

SUMMARY OF THE INVENTION

In light of the advantages and drawbacks of prior art MR devices, thepresent invention is a controllable valve assembly of the MR varietywhich is particularly useful for application in MR mountings and MRlinear dampers, for passively producing "asymmetrical" damping in thevarious operating directions. For example, the "asymmetry" may take theform of different damping rates in the "compression" and "extension"directions. In a point of novelty, this "asymmetrical" feature isachieved via various "passive" means, therefore, eliminating the need to"rapidly switch" the current applied to the valve assembly, as requiredin prior art MR devices thereby dramatically simplifying electroniccontrol needs.

In a first novel aspect, the "asymmetrical" damping characteristic isachieved by implementing a "changeable flow gap" within the controllablepassageway which is exposed to magnetic field by implementing a moveablewall portion of a magnetic return member which moves relative to anotherportion of the valve body. Preferably, the magnetic circuit is orientedsuch that magnetic body forces on the magnetic return are minimized.This "changeable gap" dimension of the controllable passageway isvariable as a function of flow direction. The "changeable gap" may beachieved by spring-loading of the wall portion of the controllable MRpassageway, such that the gap widens or narrows as a function of flowdirection, thereby changing the reluctance of the magnetic circuit and,resultantly, changing the damping characteristics of the particularvalve or device by changing the magnetic field strength acting upon themagnetically controlled fluid contained within the MR controllablepassageway.

In a second novel aspect, the "asymmetrical" damping characteristic isachieved by providing a "separate passive passageway" including a"one-way check valve" operative therewith. The passive passageway islocated in parallel relationship to the MR controllable passageway andprovides the means for preferably substantially restricting flow throughthe passive passageway in a first flow direction, yet allowingsubstantial flow in a second flow direction. This provides differingdamping properties in the first and second flow directions, therebyeliminating the need to "rapidly switch" the controllable passageway toachieve the asymmetrical damping properties, as was required in priorart MR devices. The one-way check valve mechanism may take the form of aflexure, a floating disc, a slideable annular member, a spring-loadedpoppet, a reed valve, a ball valve, or the like. Preferably, the passivepassageway is situated "outside" the magnetic circuit such that thepassive passageway is not exposed to any substantial amount of magneticflux. However, the passive passageway may be situated "within" themagnetic circuit, if the dimensions of the passive passageway are suchthat they are substantially larger than comparable dimensions of thecontrollable passageway, such that a localized zone of lower magneticfield strength is achieved adjacent to the passive passageway, whichresultantly minimizes any rheology change within the passive passageway.

In a third novel aspect, the "asymmetrical" damping characteristic isachieved by providing a "first controllable passageway" which preferablyincludes a one-way check valve operative therewith, for only allowing MRcontrollable flow in a first flow direction, and a "second controllablepassageway" preferably including a one-way check valve operativetherewith, for only allowing controllable flow in a second flowdirection. Preferably, the magnetic circuits associated with the firstand second controllable passageways provide different magneticreluctances. This provides "asymmetrical" damping properties in thefirst and second flow directions, thereby eliminating the need torapidly switch the current applied to the controllable passageways.Notably, the magnetic fields may be generated with a single or dualcoils.

In a fourth novel aspect, the "asymmetrical" damping characteristic isachieved by providing a controllable passageway which includes a"directionsensitive pole piece" which slides axially within limits toform a magnetic circuit with "changeable magnetic reluctance", whichvaries as a function of flow direction through the controllablepassageway. This provides different damping properties in the first andsecond flow directions, thereby eliminating the need to rapidly switchelectrical current.

It is an advantage of the present invention controllable MR valveassembly when used in any controllable MR device, such as a MR mountingor MR damper, that "asymmetrical" damping forces may be obtainedentirely passively.

It is another advantage when the controllable MR valve assembly is usedin a controllable MR damper or MR mounting that higher damping forcesmay be obtained in one direction (ex. extension) and lower forces in theother direction (ex. compression) without having to "rapidly switch" thecurrent, thereby minimizing control needs as compared to prior art MRdevices.

The abovementioned and further features, advantages, and characteristicsof the present invention will become apparent from the accompanyingdescriptions of the preferred embodiments and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which form a part of the specification,illustrate several key embodiments of the present invention. Thedrawings and description together, serve to fully explain the invention.In the drawings,

FIG. 1 illustrates a partial cross-sectioned side view of a controllableapparatus, such as a MR linear damper including a controllable MR valveassembly therein,

FIG. 2a and FIG. 2b illustrate bottom, and cross-sectioned side views,respectively, of a piston assembly of an embodiment of MR linear damperwhich includes a controllable valve assembly with a flexure-type one-waycheck valve,

FIG. 3a and FIG. 3b illustrate bottom, and cross-sectioned side views,respectively, of another controllable valve assembly with a flexure-typeone-way check valve,

FIG. 4a and FIG. 4b illustrate cross-sectioned side views of twodifferent piston assemblies within MR linear dampers which each includecontrollable valve assemblies with floating-disc one-way check valves,

FIG. 5a-5b and FIG. 6a-6b illustrate cross-sectioned side views ofpiston assemblies of MR linear dampers which include controllable valveassemblies with a slideable annular member acting as a one-way checkvalve,

FIG. 7a and FIG. 7b illustrate bottom, and cross-sectioned side views,respectively, of a piston assembly of MR linear damper including acontrollable valve assembly with a plurality of poppet-type one-waycheck valve,

FIG. 8a and FIG. 8b illustrate bottom, and cross-sectioned side views,respectively, of a piston assembly of a MR linear damper which includesa controllable valve assembly with a reed-type one-way check valve,

FIG. 9a and FIG. 9b illustrate approximated performance curves for thecontrollable valve assemblies incorporating a one-way check valve,

FIG. 10a and FIG. 10b illustrate cross-sectioned side views of a pistonassembly of MR linear damper which includes a controllable valveassembly with a wall portion that is moveable to provide a changeablegap and wherein FIG. 10a shows the minimum gap position while FIG. 10bshows the maximum gap configuration,

FIG. 11 illustrates a cross-sectioned side view of a piston assembly ofMR linear damper which includes a controllable valve assembly with themoveable wall portion being spring-loaded by a flexure,

FIG. 12a and FIG. 12b illustrates cross-sectioned side views of a singletube MR damper, and the piston assembly therefor, respectively, whichincludes a ball-type one-way check valve, and a plurality of coilsacting as magnetic field generators for a plurality of controllablepassageways,

FIG. 12c illustrates a Force versus Velocity performance curveillustrating actual measured performance data of the MR single-tubelinear damper of FIG. 12a including the controllable MR valve assemblyof FIG. 12b,

FIG. 13 illustrates a cross-sectional side view of a MR controllablevalve assembly including a ball-type one-way check valve,

FIG. 14a and FIG. 14b illustrate cross-sectional side views of severalMR fluid mountings including controllable MR valve assemblies withone-way check valves,

FIG. 15a-15c illustrates a cross-sectional side view, a bottom view, anda top view, respectfully, of another controllable MR valve assembly inan MR linear damper which includes a first annular controllablepassageway for flow in a first direction and a second concentric annularcontrollable passageway for flow in a second direction,

FIG. 16a illustrates a cross-sectional side view of another controllableMR valve assembly which includes a moveable wall portion,

FIG. 16b illustrates a bottom view of a flexure which flexibly supportsthe magnetic return,

FIG. 17 illustrates a cross-sectional side view of a MR fluid mountingwhich includes a moveable wall portion within the controllablepassageway,

FIG. 18a-18c illustrates a cross-sectional side view, a top view, and abottom view, respectfully, of a MR linear damper which includes aplurality of controllable passageway segments,

FIG. 19a and 19b illustrate cross-sectional side views of a MR lineardamper which includes an annular controllable passageway with a slidingpole piece which provides varying magnetic circuit reluctance as afunction of flow direction,

FIG. 20 illustrates a cross-sectional side view of a MR linear damperwhich includes multiple controllable passageways and dual coils, and

FIG. 21 illustrates a cross-sectional side view of a MR linear damperwhich includes multiple controllable passageways and a single coil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the Drawings where like numerals denote like elements,in FIG. 1, shown generally at 20a, is a first embodiment of a MR devicewhich includes the present invention MR valve 18a and which illustratesconceptually, the preferred elements contained therein. This embodimentof MR device 20a is a linear-acting MR damper, and includes a housing22a having a generally cylindrical shape and a first closed end 48a, anaperture 50a formed through a second end 48a' which is generally opposedto the first closed end 48a, and which includes an internal cavity 26alocated therein. A piston assembly 24a is slidably received within theinternal cavity 26a and subdivides the internal cavity 26a into firstand second chambers 28a, 30a, between which, the working MR fluid flows.A piston rod 25a is secured to said piston 24a and is slidably, andpreferably sealingly, received within said aperture 50a. The aperture50a preferably includes a bearing and seal assembly, as is known tothose of skill in the art. Further descriptions of such bearings andseals may be found in U.S. application Ser. No. 08/674,179 to Carlson etal. entitled "Controllable Vibration Apparatus." General descriptions ofMR linear dampers may be found in commonly assigned U.S. Pat. No.5,277,281 to J. D. Carlson entitled "Magnetortheological Fluid Dampers"and U.S. Pat. No. 5,284,330 to J. D. Carlson et al. entitled"Magntorheological Fluid Devices."

The means for attaching the piston rod 25a to the first member 21a, suchas a vehicle seat or chassis, includes rod end 27a and appropriatefasteners. Likewise, the means for attaching the housing 22a to thesecond member 23a, such as a chassis or moveable suspension member,comprises rod end 27a' and appropriate fasteners. The rod ends 27a, 27a'may include elastomer or other friction-reduced motion-accommodatingassemblies, such as ball or pin joints. A valve body 32a within thepiston 24a contains at least a portion of the magnetic circuit 40a. Amagnetic circuit 40a is capable of carrying a magnetic flux φ (arepresentative approximate flux line is labeled as the magnetic circuit40a as will be the case with all embodiments described herein). Itshould be recognized that a substantial portion of the magnetic flux φis carried within the magnetic circuit 40a.

A controllable passageway 42a is located adjacent to the valve body 32aand in the vicinity of the magnetic circuit 40a. Preferably, thecontrollable passageway 42a passes "through" the valve body 32a and isannular shaped. However, it may pass "about" the valve body 32a, as isknown to those of skill in the art. Such valves where the controllablepassageway passes "about" the piston assembly are described in U.S. Pat.No. 5,277,281 to J. D. Carlson et al. The controllable passageway 42a iscapable of user-controllable flow or programmed (via a computeralgorithm) flow. The working MR fluid 44a is contained within, andpreferably substantially fills, the controllable passageway 42a, thefirst chamber 28a, and the second chamber 30a. The MR fluid 44a containssoft-magnetic particles dispersed in a liquid carrier of preferably lowviscosity. One such fluid is described in U.S. Pat. No. 5,578,238 toWeiss et al. entitled "Magnetorheological Materials Utilizing SurfaceModified Particles."

A magnetic flux generator, preferably a coil 46a, is manufactured from amagnet wire circumferenitially wound about a cylindrical bobbin. Thecoil 46a is preferably located within, and supported by, the valve body32a and generates a magnetic flux φ which is then carried by themagnetic circuit 40a. The magnetic flux is directed by pole pieceportions of the valve body 32a to act upon the MR fluid 44a contained inthe controllable passageway 42a to provide user controllable flow. Inother words energizing the coil 46a with electrical current (preferablyDC) will create a magnetic field within the magnetic circuit 40a whichwill cause a "rheology" change, i.e., an alignment of the soft-magneticparticles in the MR fluid 44a in the controllable passageway 42a. Theresult is a restriction of flow through the controllable passageway 42a.Notably, the MR fluid 44a located elsewhere, such as in chambers 28a,30a is not exposed to any significant magnetic field and does notundergo a rheology change.

In this first aspect, the means for providing "asymmetry" is provided bya passive passageway 36a which is preferably arranged in parallelrelationship to the controllable passageway 42a. The passive passageway36a includes a one-way check valve 34a operative therewith. The checkvalve 34a may be situated at the ends of the passive passageway, orin-between, so as to allow substantial flow of MR fluid 44a in a firstflow direction associated with movement of the piston 24a in a firstlinear direction (example: compression) and substantially restrict flowof the fluid 44a in a second flow direction associated with movement ofthe piston 24a in a second linear direction (example: extension).Functionally, the one-way check valve 34a acts as a bypass in onedirection, allowing a substantially portion of the MR fluid 44a tobypass the controllable valve 42a. Preferably, the cross-sectional areaof the passive passageway 36a will be greater than that of thecontrollable passageway 42a. Notably, if a DC bias is applied to thecoil 46a, substantially all flow of MR fluid 44a will be through thebypass, as the fluid 44a in the controllable passageway 42a will begenerally "locked up." Although, shown with the one-way check valve 34amaking damping in extension higher, in some applications, it may bedesirable to reverse the check valve 34a, such that the compressionstroke achieves higher damping.

In one variation of the present invention, the passive passageway 36a islocated in a position which is "outside" of the magnetic circuit 40a,such that the MR fluid 44a passing through said passive passageway 36ais not exposed to any "substantial" amount of said magnetic flux φ i.e.,magnetic field strength. The passive passageway 36a may either passthrough the valve body 32a, or, alternatively, pass about the valve body32a. Both embodiments are described in detail herein. In general, it isdesirable that the passive passageway 36a be exposed to less than about10% of the magnetic field strength exposed to the controllablepassageway 42a. Notably, later herein, with reference to FIG. 8a and 8b,another novel embodiment will be described wherein the passivepassageway is located "within" the magnetic circuit and adjacent to anarea of the controllable valve exposed to a "substantial" magneticfield, yet is still operative to provide asymmetric damping.

Again referring to FIG. 1, but also referring to all other embodimentsherein, an optional passive shaping passageway 41a may be added inparallel to the controllable valve 42a. This may be desirable tominimize harslhess. It may take the form of a port through the piston24a or designed-in blow-by around the wear band 64a (See 41b of FIG.2b).

Wire leads 31a provide the low voltage control signal (generally 12 VoltDC and electrical current of about several amps or less) from thecontroller 33a to the coil 46a. Optional sensor or sensors 35a mayprovide the appropriate input signal to the controller 33a, if needed,for feedback or other control. For example, some types of control mayrequire only displacement information while others require displacement,acceleration, or even velocity information. It may be desirable toadaptively control the level of DC current applied based upon some timeaveraged sensor inputs.

Descriptions of various types of semi-active control for MR dampers, ERdampers, Semi-active (hydraulic) dampers, or the like, may be found inU.S. application Ser. No. 08/534,078 to Catanzarite entitled"Controllable Seat Damper System and Control Method Therefor" and U.S.application Ser. No. 08/639,139 to Catanzarite entitled "Control Methodfor Semi-Active Damper", as well as in U.S. Pat. No. 5,390,121 to Wolfeentitled "Banded On-Off Control Method for Semi-Active Dampers."Flowever, it should be understood, that the "asymmetric" dampingprovided by the present invention, is preferably provided in a "passive"fashion through use of the one-way check valve 34a and optional passiveshaping passageway 41a in combination with the controllable passageway42a. Resultantly, sophisticated control needs are preferably minimizedor even eliminated. For example, using the various novel means forproviding "asymmetry" described herein, only a DC bias current needs tobe applied to the coil 46a, as opposed to the Alternating Current (AC)or a rapidly switching DC current needed for semi-active active controlin prior art MR devices. This level of the DC bias may be adjusted by auser operated damping level adjustment switch 52a, dial, or the like.Notably, no "rapid" switching in real time is required to achieve the"asymmetrical" damping. It should be understood, however, in some cases,control may still be desired, such as to combat such conditions asendstop collisions (where the piston may contact either end of thedamper). A useful control algorithm for reducing endstop collisions maybe found in U.S. Pat. No. 5,276,622 to Miller et al.

The damper 20a is shown with a gas charged accumulator, which provides aspring component, as well as a gas charge, to the damper 20a. Theaccumulator includes a charge chamber 29a which is separated from secondfluid chamber 30a by a slideable partition 37a, such as the slideableand sealed partition shown. Appropriate gas charging is achieved viafill valve 39a. A certain level of pressure charge (approx. 100 psi ormore) is needed to combat fluid cavitation under certain dampingconditions.

FIG. 2a and FIG. 2b illustrate a first embodiment of piston assembly 24bincluding a controllable MR valve 18b therein, and which also includes aflexure 34b interactive with the passive passageway 36b acting as themeans for providing asymmetric damping. FIG. 2a is a bottom view withflexure 34b removed for clarity. As before, the piston 24b attaches topiston rod 25b and is slideable in housing 22b. The valve body 32b ismade Up of a center portion 56a and an annular ring 58b, both of whichare preferably manufactured from a softmagnetic material, such aslow-carbon steel. Preferably, nonmagnetic welds 60b, spacers or the like(preferably 3 or four equally spaced about the top entrance ofcontrollable passageway 42b) rigidly secure the ring 58b to the centerportion 56b. A coil 46b of suitable number of winds is woundcircumferentially about the center portion 56b, or about a bobbin, iftwo piece construction of the center portion 56b, is used. Leads 31battach to coil 46b and exit through rod 25b, Appropriate shaft seal 62bprevents escape of MR fluid. The ring 58b and center portion 56binteract radially to form the annular-shaped controllable passageway 42bwhich passes through the valve body 32b.

A wear band 64b, which is preferably steel coated with the appropriatefriction-reducing treatment encircles the outer periphery of ring 58band provides the appropriate clearance between the piston 24b andhousing 22b. Notably, a passive shaping passage 41b may be formedbetween the outer periphery of wear band 64b and the inner wall ofhousing 22b to allow some designed passive MR fluid flow therethroughwhich reduces or eliminates harshness. The passive passageway 36b islocated in parallel relationship to the controllable passageway 42b andpreferably comprises a plurality of holes through the valve body 32b.

The flexure 34b is preferably a disc-shaped member, manufactured fromspring material which exhibits low magnetic permeability, and is securedto the center portion 56b of valve body 32b by rivet, screw, weld,adhesive, or the like. The flexure 34b is of sufficient bending(cupping) compliance to bend and open in the extension directionrelative to the valve body 32b, thereby allowing a substantial amount ofMR fluid to flow therethrough in the extension direction (in directionof small arrows) and providing minimal or shaped damping, in that theshaping can be designed in. Minimal adjustment is achievable in theextension direction, as the majority of flow is through the passivepassageway 36b having the one-way check valve 34b. Contrarily, the levelof damping may be adjusted in the compression direction based uponadjusting the DC bias to the coil 46a, via a damping level switch orappropriate computer program. Flow of MR fluid is substantiallyrestricted through the passive passageway 36b in compression, becausethe flexure 34b acts as a one-way check valve in that direction, and issubstantially closed. The magnetic circuit 40b in this embodiment iscarried within the center portion 56b, in ring 58b, in the MR fluidwithin the annular controllable passageway 42b, and in the wear band64b. Of course this assumes that the wear band 64b is manufactured forma high magnetic permeability material. Notably, the passive passageway36b passes through the valve body 32b, yet is substantially free fromexposure to the magnetic field, as it receives generally less than about10% of the magnetic field strength, and may be as low as 1% of the fieldstrength which is exposed to the controllable passageway 36b. Notably,the steel surrounding the passive passageways 36b will shunt any fieldaround the passive passageway 36b rather than through it. Generally,these passive passageways 36b are high reluctance areas. Therefore, theMR fluid is substantially free to flow in the passive passageway 36b inthe extension direction. Although not shown, stacks of flexures 34bcould be used for providing progressive relief.

FIG. 3a and FIG. 3b illustrate a similar embodiment to FIG. 2b, exceptthat the flexure 34c is restrained between the center portion 56c of thevalve body 32c and a step formed on pistonl rod 25c. A local relief 66cmay be added to equalize the flow between the various plurality ofpassive passageways 36c and allow ease of MR fluid flow to the outermostradial portion of the flexure 34c. Notably, this configuration offlexure 34c which is interactive with the passive passageway 36c, allowscontrollability in extension by restricting substantially all MR fluidthrough the controllable passageway 42c in extension while allowingrelatively free flow in compression through the passive passageway 36c.An asymmetric damping performance curve, such as is approximated by FIG.9b, may be achieved by such a valve construction utilizing a flexure 34cacting as a one-way check valve operative with a passive passageway 36c.This eliminates the need to rapidly switch the current to the MR valveto achieve different characteristics in compression and extension.Again, in this embodiment, the passive passageway 36c passes through thevalve body 32c yet is substantially free from exposure to the magneticfield.

FIG. 4a and FIG. 4b illustrate two other embodiments of controllable MRvalve assemblies 18d. 18e included within piston assemblies 24d. 24e oflinear-acting dampers 20d, 20e, similar to the FIG. 3a and FIG. 3bembodiments. The difference is that, rather than including a flexure asthe one-way check valve, the one-way check valve mechanism is comprisedof floating discs 34d, 34e. The floating discs 34d, 34e are preferablylocated adjacent to an end of the passive passageway 36d, 36e and themovement of the discs 34d, 34e along the axial axis is restrained withinpredetermined limits by at least one selected from a group of componentsconsisting of: a) the valve body 32d, 32e, and b) a piston rod 25einterconnected to said valve body 32e. Likewise, pins or otherprotrusions from the valve body 32e or piston rod 25e may be employed tolimit motion of the discs 34d, 34e.

For example, referring to FIG. 4a, the floating disc 34d would bemanufactured from a metal, plastic, other polymer material, orcombinations thereof, and would be free to move (float) within gap 68dformed between the valve body 32d and the retainer 70d. The retainer 70dincludes several radially-protruding tabs 72d formed thereon to limitexcessive axial downward movement of disc 34d. In the extensiondirection, the disc 34d will rest against tabs 72d and flow of the MRfluid will be about the disc 34d exiting between the disc 34d and valvebody 32d. Contrarily, during the compression stroke, the disc 34d willmove vertically and seal off the passive passageways 36d.

Disc 34e in FIG. 4b operates in substantially the same fashion, exceptit floats between the step in piston 25e and the valve body 32e.Notably, this embodiment allows controlled damping in extension andsubstantially free flow (low damping) in compression, as opposed to theFIG. 4a embodiment, which allows controllable damping in compression andsubstantially free flow in extension. Notably, in both embodiments, thepassive passageways 36d, 36e pass through the valve body 32d, 32e yetare substantially free from exposure to the magnetic field.

FIGS. 5a, 5b, 6a, and 6b illustrate several embodiments of controllablevalves 18f, 18g included within piston assemblies 24f, 24g oflinear-acting dampers 20f, 20g. In particular, the embodiment describedin FIG. 5a and 5b was reduced to practice. In each of these embodiments,the passive passageways 36f, 36g are situated around, and flow "about",the valve body 32f, 32g, and are closed off in the compression directionby one-way check valve mechanisms comprising slideable annular members34f, 34g. The annular members 34f, 34g are located adjacent to, andencircle, a radial outer periphery of the valve bodies 32f, 32g and areinteractive with the valve bodies 32f, 32g to control flow of the MRfluid through the passive passageways 36f, 36g. The annular members 34f,34g are restrained within predetermined limits by lip portions 74f,74f', 74g, 74g' formed on, and protruding radially from, the valvebodies 32f, 32g.

The one-way check valve mechanism is accomplished by allowing flowbetween the rings 74f, 74g of valve bodies 32f, 32g and the annularmembers 34f, 34g in one direction and substantially closing off flow inthe other. Flow in the extension direction is allowed in the passivepassageways 36f, 36g by having the passageways 36f, 36g at leastpartially formed by one selected from a group of relieves consisting of:a) a relief 66f formed in the annular member 34f, and b) a relief 66gformed in the valve body 32g. In FIG. 5a, 5b, each of the relieves 66fin the annular member 34f comprise a square, rectangular,semicircular-shaped, or other wise contoured slot formed in the bottomaxial edge of the annular member 34f. Preferably, a plurality ofradially-spaced slots are used. In the FIG. 6a, 6b embodiment, therelief 66g is comprised of a spline plunged into the valve body 32g.Likewise, preferably, a plurality of radially-spaced splines areemployed. The splined relief 66g only extends part way across the radialperipheral surface of the ring 58g.

For example, FIG. 6a illustrates the position of the annular member inthe compression direction. The annular member 34g is located in sealedengagement with the lip 74g, covering recess 66g and, thereby,substantially restricting MR fluid flow in compression through thepassive passageway 36g. Contrarily, FIG. 6b illustrates the annularmember 34g in the other terminal position, during the extension stroke,whereby the passive passageway 36g is opened up and MR fluid may flowabout the valve body 32g. Likewise, FIG. 5a illustrates the annularmember 34f in the position during the compression stroke, where the flowof MR fluid is cut off by annular member 34f contacting lip 74f. Inextension (FIG. 5b) the flow of MR fluid is substantially unrestrictedand MR fluid is substantially free to flow through passive passageway36f and through slot relief 66f.

In each of these embodiments FIG. 5a-FIG. 6b, controllable flow isallowed in compression, and substantially free flow is permitted inextension, thereby providing a controllable damping force (which mayrange from a high value to a low value depending upon electrical currentsupplied to the coil) in compression and a low damping force inextension. It should be understood, that this relationship may bereversed by simply reversing the orientation of the annular member 34fin FIG. 5a, and by cutting the relieves 66g into the upper portion ofvalve body 32g in the FIG. 6a embodiment instead of the lower portion.In each of these embodiments including an annular member 34f, 34g, thecoil 46f, 46g, and the magnetic circuit 40f, 40g are preferably orientedsuch that the passive passageways 36f, 36g are substantially free fromexposure to the magnetic field.

FIGS. 7a and 7b illustrate another embodiment of controllable valve 18hincluded within piston assembly 24h of a linear-acting damper 20h. Inthis embodiment, the passive passageway 36h passes through the valvebody 32h and includes a one-way check valve which takes the form of aspring-loaded poppet 34h. Preferably, the poppets 34h are spaced on acircular pattern inside the preferably annular controllable passageway42h. The poppet 34h comprises spring 43h and poppet body 45h which sealsin tapered opening in passive passageway 36h. Preferably, there are aplurality of radially-spaced passive passageways 36h and a plurality ofspring-loaded poppets 34h interactive therewith, to close off flow of MRfluid in the extension direction. Preferably, the controllablepassageway 42h comprises an annular-shaped member and the magnetic fieldis located and oriented such that the poppets 34h and passive passageway36h are not exposed to any substantial magnetic field. Preferably, thepoppet body 45h and spring 43h would be nonmagnetic.

FIGS. 8a and 8b illustrate another embodiment of controllable valve 18jincluded within piston assembly 24j of a MR linear-acting damper 20j. Inthis embodiment, the passive passageways 36j has a one-way check valveinteractive therewith, which takes the form of a reed-type valve 34j.Freferably, there are a plurality of reed valves 34j and a plurality ofradially-spaced passive passageways 36j. The means for providing"asymmetric" damping, in this embodiment, comprises a passive passageway36j arranged in parallel relationship to the controllable passageway42j. The passive passageway 36j includes a one-way check valve operativetherewith for substantially restricting flow of the MR fluid in a firstflow direction (ex. extension) through the passive passageway 36jassociated with movement of the piston assembly 24j in a firstdirection, yet allowing substantial flow of MR fluid in a second flowdirection (ex. compression) associated with movement of the pistonassembly 24j in a second direction. In contrast to the previousembodiments, the passive passageway 36j is situated "within" themagnetic circuit 40j, such that the passive passageway 36j could receivesubstantial exposure to said magnetic field, as does the controllablepassageway 42j. However, flux will avoid the passive passageways 36jbecause they represent larger reluctance as compared to the controllablepassageways 42j.

In more detail, preferably, the passive passageways 36j are separatedfrom the controllable passageway 42j via partition means, such aspartition tube 76j. The tube 76j is inserted and separates the passivepassageway 36j from the controllable passageways 42j along the length ofthe valve body 32j. The dimensions of the passive passageway 36j arepreferably substantially larger than the controllable passageway 42j. Byway of example, the dimensions of the annular controllable passageway42j might be between about 0.02 in to 0.06 in (0.5 mm to 1.5 mm) whilethe dimensions of the passive passageway 36j would be between about 0.08in to 0.20 in (2 mm to 5 mm). By making the passive passageway 36jpreferably much larger, the flux density (localized field strength)therein is significantly reduced, thereby, reducing substantially therheology change experienced therein, and allowing substantially freeflow of MR fluid through the passive passageway 36j in the uncheckeddirection (compression) even though the passive passageway is situated"within" the magnetic circuit.

FIG. 9a and FIG. 9b illustrate approximate Force v. Velocity performancecurves for the controllable valve assemblies before described.Alternatively, these may be thought of as pressure-flow profiles. In thecase where controllability in compression is desired, FIG. 9aillustrates the approximated profile. The slope or character of the lowvelocity region 78 (occurring at low fluid flow velocities) is dictatedby the passive shaping passageway. If there is fluid inertia associatedwith this orificing/passageway, it will play a more important role athigher velocities. Otherwise, the effect of this orificing/passagewaywill be seen at all velocities. In other words, a fluid inertia can bedesigned into the passive shaping passageway to limit its effects athigher velocities.

The slope or character of the controlled region 80 is largely dictatedby the viscosity of the MR fluid and the nature (shape, length,entrances, etc.) of the MR controlled passageway. The overall level ofdamping may be varied from a low value to a high value H, depending uponthe current supplied to the coil. The family of curves shown isillustrative of four different applied currents, from zero current tomaximum current.

The force at which break point 82 occurs is largely dictated by theparameters of the one-way check valve (ex. the thickness and stiffnessof the flexure disks 34b, 34c (FIG. 3a and 3b) and the level ofprestressing of the disks 34b, 34c, the gap 68d in the FIG. 4aembodiment, the dimensions between lips 74f, 74f" and lips 74g, 74g' anddimensions of slot relieves 66f or spline relieves in the FIG. 5a-6bembodiments, the characteristics of poppet 34h, i.e., shape, stiffness,etc. in the FIG. 7a, 7b embodiment, and the dimensions of passivepassageway 36j and stiffness/prestressing of reed valve 34j in the FIG.8a, 8b embodiment. The character of flow relief region 84 is dictated bythe nature of the orificing/passive passageway, stiffnesscharacteristics of one-way check valves and MR fluid properties(viscosity, exposure to magnetic field, etc.).

FIGS. 10a, 10b and 11 illustrate another embodiment of controllablevalve 18k, 18m within a piston assemblies 24k, 24m of a MR device, suchas the linear-acting MR dampers 20k and 20m. The piston assemblies 24k,24m act a partitions subdividing the internal cavities 26k, 26m into afirst fluid chamber 28k, 28m and second fluid chamber 30k, 30m. Themeans for providing "asymmetric" damping in controllable valves 18k, 18mcomprises providing a "changeable gap" within said controllablepassageways 42k, 42m whose dimension (gap thickness) is variable as afunction of the flow direction of the MR fluid between first and secondchambers 28k, 28m and 30k, 30m. As will become apparent, thecontrollable valve assembly 18k, 18m may be used singly, or within a MRlinear damper or MR mounting.

In particular, a spring 84k, 84m preferably causes spring loading of awall portion 86k, 86m of the controllable passageways 42k, 42m whichallows the wall portion 86k, 86m to move as a function of flow directionand, thus, vary the gap dimension associated with the controllablepassageways 42k, 42m as a function of flow direction. Providing aspring-loaded wall portion 86k, 86m causes the changeable gap dimension(ex. tg) to be larger in a first flow direction (ex. compression shownin FIG. 10b) and smaller in a second flow direction (ex. extension shownin FIG. 10a) and, resultantly, produce more restricted flow of the MRfluid 44k, 44m in the second direction (ex. extension) than in the firstdirection (ex. compression). This creates higher damping forces in thefirst flow direction than in the second flow direction.

In the FIG. 10a and FIG. 10b embodiment, the spring 84k is a coil-typespring which provides a spring force between cup 58k and shaft 25k. Thec-clip 88k maintains the appropriate precompression of the spring 84kand forces the cup 58k into intimate contact with nonmagnetic spacer73k, 73m between cup 58k and center portion 56k. In the compressiondirection, the cup 58k moves relative to the center portion 56k,axially. This causes the gap thickness tg to get larger. As a result,the damping forces fall off significantly, as the magnetic reluctance ofthe magnetic circuit 40k contained in the piston assembly (partition)24k, 24m increases. This is because the magnetic circuit's reluctance isstrongly affected by the gap thickness tg. Moreover, the larger gapthickness tg also changes the hydraulic lever and reduces drag therebyfurther amplifying the effect. By varying the angle θ, the degree ofdifference in damping in compression and extension may also be adjusted.It should be understood that the current to coil 46k, 46m generates themagnetic field in magnetic circuit 40k, 40m, and that that current isgenerally constant, but may vary between a min and max level to adjustthe damping level in the controlled direction. Changing the gapthickness tg changes the circuit reluctance as a function of flowdirection, therefore, providing "asymmetry" in damping. In the FIG. 11embodiment, the spring loading of wall portion 86m is provided by aflexure 84m. The cup 58m is preferably spot welded to the shaft 25m.This embodiment operates substantially as described with reference toFIG. 10a, 10b, except that the spring loading is provided by flexure84m. It should be understood that the magnetic circuits 40k, 40m areoriented such that magnetic body forces between the cup 58k, 58m andcenter portions 58k, 58m are minimized.

FIG. 12a and 12b illustrate an embodiment of damper 20n and controllablevalve assembly 18n that was reduced to practice experimentally. Thedamper 20n is a single tube linear-acting MR damper (linear referring toproviding damping forces being generated along a linear axis) whichincludes a piston assembly 24n having a controllable valve assembly 18nreceived within housing 22n. In this embodiment, the controllable valveassembly 18n includes a first controllable passageway 42n forcontrolling flow of the MR fluid 44n in a first flow direction(compression) and a second controllable passageway 42n' for controllingflow in a second flow direction (extension). A passive passageway 36nincluding a ball valve 34n operative therewith comprising a one-waycheck valve is arranged in parallel relationship with the particularcontrollable passageway 42n, 42n' that is "operative" for that flowdirection.

For example, as shown in FIG. 12a, the ball valve 34n operative with thepassive passageway 36n closes off the lower passive passageway 36n' (asshown), such that the MR fluid 44n is forced to flow through the secondcontrollable passageway 42n'. Flow through the upper passive passageway36n" is substantially unrestricted. Likewise, as shown in FIG. 12b, whenthe damper is in compression, the ball valve 34n closes off the upperpassive passageway 36n" (as shown) and the MR fluid is forced to flowthrough the first controllable passageway 42n. It is notable that thecontrollable passageways 42n, 42n' and the passive passageways 36n',36n" preferably share at least a common ingress 90n into the valve body32n, and may also share a common egress 92n from the valve body 32n. Thecontrollable passageways 42n, 42n' pass about baffle plates 92n, 92n'for exposing more of the MR fluid to the magnetic flux, as illustratedby magnetic circuits 40n, 40n'. The ball valve 34n comprises a sphericalball 94n which seals in seats formed in the baffle plates 92n, 92n'.FIG. 12c illustrates actual test data of the performance of the damper20n of FIG. 12a. This dual-coil embodiment has some key advantages. Forsmall deflections, the ball floats to provide a "null band." When the"null band" is exceeded, the ball 94n seats in seat formed in baffleplate 92n, 92n'. Then the proper DC bias may be commanded to provide theappropriate controlled damping in each flow direction.

Each of the previous embodiments are soft in a first direction and stiffin a second for all conditions. This embodiment departs from thatscenario by allowing the damper to be stiff in a first direction, andsoft in the second for most conditions, yet when a high level of dampingis required in the second direction, the level of damping may beincreased. This higher level of damping in the second direction may bedesirable for reacting to transient or other conditions. The dualcontrollable passageways 42n, 42n' comprise one acting to control flowin a first direction, and another controlling flow in a seconddirection. This particular embodiment is particularly well suited forimplementing semi-active "skyhook" control in suspension systems withvastly simplified control and sensor requirements as compared to priorart systems. FIG. 12c illustrates that in extension, the family ofperformance curves shown are achievable by applying DC bias to coil46n', thereby generating a magnetic flux which acts upon the MR fluid inthe second controllable passageway 42n'. Likewise, in compression, thefamily of performance curves shown are achieved by applying DC bias tocoil 46n, thereby generating a magnetic flux which acts upon the MRfluid in the first controllable passageway 42n. Notably, the passivepassageways 36n, 36n', 36n" are preferably located "outside" of themagnetic circuits 40n, 40n', such that they are not exposed to anysubstantial magnetic fields.

FIG. 13 illustrates a controllable valve assembly 18p of the two-wayacting type (designed to accommodate MR fluid flow in both directions),which comprises a valve body 32p having at least a portion of a magneticcircuit 40p contained therein, the magnetic circuit which is capable ofcarrying a magnetic flux φ, a controllable passageway 42p adjacent tothe valve body 32p and, preferably, passing through it. The controllablepassageway 42p is located within the magnetic circuit 40p and exposed tothe magnetic flux φ generated by the magnetic field generator (coil46p). A MR fluid 44p is contained in the controllable passageway 42p,and also in the ingress and egress ports 90p, 90p'. A magnetic fluxgenerator, which is preferably the afore-mentioned coil 46p, is formedby wrapping a magnet wire circumferentially about a bobbin 96b. Thegenerated magnetic flux φ is carried by the magnetic circuit 40p and isdirected by pole pieces 95p, 95p' to act through the MR fluid 44pcontained in the controllable passageway 42p. This generates therheology changes in the MR fluid 44p within said controllable passageway42p, thereby restricting flow of MR fluid 44p through the controllablepassageway 42p.

The means for providing "asymmetric" damping across said controllablevalve assembly 18p and, thereby, creating a higher pressure differentialacross the controllable valve 18p in a first flow direction (1st), and alower pressure differential in a second flow direction (2nd), withoutrapidly controlling the magnetic flux φ within the magnetic circuit 40pcomprises a one-way check valve, such as a ball valve 34p. As a result,higher damping forces are created in the first flow direction (1st) andlower damping forces in said second flow direction (2nd). It should bereadily apparent that this same configuration of valve 18p, whichincludes the ball-type check valve 34p may be used in a MR fluidmounting and a MR linear damper as well, as are illustrated in FIG. 12aand FIG. 14a. In more detail, in this embodiment, a stationarily-mountedbaffle plate 92p is secured between pole pieces 95p, 95p' by preferablynonmagnetic puck-shaped spacers 93p. The spacers 93p locate and securethe baffle plate 92p, yet do not appreciably restrict the flow of the MRfluid 44p, and do not appreciably affect the magnetic circuit 40p.

The controllable passageway 42p passes "about" the baffle plate 92p forexposing more of the MR fluid 44p to the magnetic flux φ contained inthe magnetic circuit 40p. The ball valve 34p comprises a preferablyspherically-shaped ball 94p, a circular-shaped seat 98p formed in thebaffle plate 92p, and means for restraining movement of the ball 34pwithin limits, such as pins 91p. The ball valve 34p is operative withthe passive passageway 36p is closed off by the ball 34p when MR fluid44p is flowing in the first direction (1st), thereby, forcing the MRfluid 44p through the controllable passageway 42p, where the dampinglevel, i.e., the level of restriction, may be adjusted betweensubstantially unrestricted flow and substantially no flow depending uponthe amount of electrical current supplied to leads 89p. Contrarily, whenthe MR fluid 44p is flowing in the second direction (2nd), the ball 34pmoves to the position indicted by the dotted circle C, and flow of MRfluid 44p is substantially unrestricted through the passive passageway36p. Flow though the controllable passageway 42p in the second direction(2nd) is generally restricted, as there is generally always a DC biasapplied. Notably, even when no DC bias is applied, the flow resistancethrough the passive passageway 36p is generally somewhat less than thatof the controllable passageway 42p such that the majority of flow isthrough the passive passageway 36p. Preferably, end connectors 99p, 99p'are used to connect to the hoses 97p, 97p' of the system where the valve18p is used to control flow. It should be noted, that in thisembodiment, the passive passageway 36p passes through the valve body 32pand is located "outside" the magnetic circuit 40p such that the fluid inthe passive passageway 36p is not exposed to any substantial amount ofmagnetic flux φ.

FIG. 14a and 14b illustrate several embodiments of MR fluid mountings20q, 20r which are capable of providing "asymmetric" damping withouthaving to rapidly switch the current to the coil, as required in priorart MR fluid mountings. The controllable MR fluid mountings 20q, 20rcomprise a housing member 22q, 22r, an inner member 24q, 24r, a flexiblemember 38q, 38r interconnecting between said inner member 24q, 24r andsaid housing 22q, 22r, means for interconnecting the inner member 24q,24r to a first moveable member 21q, 21r (such as an engine or enginebracket), and means for connecting the housing 22q, 22r to a secondmoving member 23q, 23r (such as a chassis or frame). An internal cavity26q, 26r housed within said mounting 20q, 20r is subdivided by a divider47q, 47r into first fluid chambers 28q, 28r and second fluid chambers30q, 30r.

A controllable passageway 42q, 42r which is capable of controllable flowis operative between the first fluid chambers 28q, 28r and second fluidchambers 30q, 30r. A MR fluid 44q, 44r substantially fills thecontrollable passageways 42q, 42r, first chambers 28q, 28r, and secondchambers 30q, 30r. The magnetic circuit 40q, 40r is preferablysubstantially contained within the divider 47q, 47r and is capable ofcarrying the magnetic flux which is generated by magnetic fluxgenerators, such as coils 46q, 46r. The coils 46q, 46r are locatedadjacent to the dividers 47q, 47r for generating a magnetic flux whichis carried by magnetic circuits 40q, 40r and which are directed by polepieces 95q, 95q' and 95r, 95r' to act upon the MR fluid 44q, 44r withinthe controllable passageway 42q, 42r.

The means for providing "asymmetric" damping comprises a one way checkvalve, such as a ball valve 34q, or spring-loaded poppet 34r, where apressure differential between the first chamber 28q, 28r and the secondchamber 30q, 30r in a first flow direction (compression) is higher thana pressure differential in a second flow direction (extension). This isaccomplished passively, without having to rapidly control (switch) theflux φ in the magnetic circuits 40q, 40r. In each of these embodiments alow stiffness diaphragm 87q, 87r partially defines the second chamber30q, 30r. Further descriptions of MR fluid mountings may be found incommonly assigned U.S. Pat. No. 5,398,197 to J. D. Carlson et al.

FIG. 15a-15c illustrate another configuration of controllable valve 18twhich finds application in an MR device, such as a linear-acting MRdamper 20t. Likewise, the construction of valve 18t, described hereinmay be adapted for use in a MR fluid mounting. The controllable damper20t is comprised of an internal cavity 26t, a partition, such as apiston assembly 24t, or the like, subdividing the internal cavity 26tinto a first fluid chamber 28t and a second fluid chamber 30t. A "first"controllable passageway 42t which is capable of controllable flow isinterconnected between the first fluid chamber 28t and the second fluidchamber 30t. A "second" controllable passageway 42t', which is alsocapable of controllable flow, is also interconnected between the firstfluid chamber 28t and the second fluid chamber 30t. A MR fluid 44t iscontained in first controllable passageway 42t, second controllablepassageway 42t', first chamber 28t, and second chamber 30t. A firstmagnetic circuit 40t, preferably having a first (higher) reluctance, iscontained within the piston assembly 24t (partition), and is capable ofcarrying a first magnetic flux. Likewise, a second magnetic circuit40t', preferably having a second (lower) reluctance, is contained in thepiston assembly 24t (partition), and is capable of carrying a secondmagnetic flux. A magnetic flux generator, in the form of a single woundcoil 46t, is located adjacent to the piston assembly 24t (partition) andgenerates the first and second magnetic flux φ, φ' which are carried bythe first and second magnetic circuits 40t, 40t'. These fluxes φ, φ' aredirected by pole pieces 95t, 95t' to act upon the MR fluid 44t containedin the first and second controllable passageways 42t, 42t'. It should benoted that a single coil 46t generates both of the magnetic fluxes φ, φ'within magnetic circuits 40t, 40t'. Controllability is provided byadjusting the DC bias to coil 46t to control flow therein.

A first one-way check valve 34t is operative with said firstcontrollable passageway 42t, thereby providing "asymmetric" damping as afunction of flow direction, by allowing flow in a first direction 1st,and substantially restricting flow in a second flow direction 2nd withinthe controllable passageway 42t. A second one-way check valve 34t' isoperative with the second controllable passageway 42t', and provides"asymmetric" damping as a function of flow direction, by allowing flowin the second flow direction 2nd and substantially restricting flow inthe first flow direction 1st. The check valves 34t, 34t' preferablycomprise spring-type flexures, which are preferably disc shaped. Thefirst check valve 34t is preferably secured to valve body 32t by aappropriate means, such as a screw, weld, adhesive, or the like. Formedin check valve 34t are spaced-apart slot segments which allow asubstantial flow of MR fluid 44t through the second controllablepassageway 42t' in a second flow direction 2nd. Likewise, second checkvalve flexure 34t' is secured to valve body 32t by a step on piston rod25t.

The novelty in this embodiment lies in the combination of a firstcontrollable passageway 42t for allowing controlled damping in a firstdirection 1st and a second controllable passageway 42t' allowingcontrolled damping in a second direction 2nd. Notably, both the firstand second passageways 42t, 42t' are acted upon by a "common" magneticfield generated by a "common" coil 46t. The reluctance of magneticcircuits 40t, 40t' are preferably different, thereby providing lessresistance to flow of MR fluid 44t in one flow direction than in theother.

In this embodiment, the piston assembly 24t is constructed from aannular outer ring 58t, an annular inner ring 58t', and a center portion56t, all of which are preferably manufactured from magnetically-softmaterial, such as low carbon steel. Preferably, nonmagnetic welds 60tinterconnect outer ring 58t and inner ring 58t'. Likewise preferably,nonmagnetic welds 60t' interconnect the inner ring 58t and the centerportion 56t. The check valve flexures 34t, 34t', which are interactivewith controllable passageways 42t, 42t', are preferably manufacturedfrom suitable spring-steel material, or the like, and are of theappropriate stiffness to provide the appropriate dampingcharacteristics. Optional wear bands 64t, which preferably include afriction reducing surface treatment, are in sliding contact with thehousing 22t of the single-tube linear MR damper 20t. Although, flexuresare shown, many of the other one-way check valves described herein couldalso be adapted.

FIG. 16a-b illustrates another embodiment of valve assembly 18v, whichutilizes a valve similar to that described with reference to FIG. 11.The main difference is that the valve 18v is configured as a stand alonein FIG. 16a for controlling MR fluid flow between any two fluidchambers. The FIG. 17 embodiment is another MR mounting 20wincorporating the type of valve described with reference to FIG. 16a.The elements in valve 18v are similar to the FIG. 13 embodiment, exceptthat the means for providing "asymmetry" is provided by a moveable wallportion 86v which is moveable, in a generally axial direction, relativeto pole pieces 95v, 95v', and moveable as a function of flow rate andflow direction. The bullet-shaped magnetic return 92v is flexiblysuspended relative to the valve body 32v, and is manufactured ofsuitable soft-magnetic material, and functions to complete the magneticcircuit 40v. The spring 84v preferably takes the form of a nonmagneticflexural spider, as is shown in FIG. 16b, and has a plurality of springelements 85v. Additionally, an extra spring similar to spring 84v may bepositioned, and secured, at the other end of magnetic return 92v forstabilizing any sideways movement. Flow in the direction shown by thearrow causes MR fluid 44v to move the return 92v in the downwarddirection relative to the pole pieces 95v, 95v', thereby increasing thegap thickness tg. This quickly increases the reluctance of the magneticcircuit 40v and, thereby, lowers the MR effect causing less of arestriction of the MR fluid 44v. Conversely, in the other flow direction(opposed to arrow shown), the MR effect is increased, thereby,increasing the flow resistance. The angle imposed on the outer surfacesof return 95v and inner surfaces of pole pieces 95v, 95v' may beadjusted to provide more variation in the two flow directions. However,it is desirable to keep the angle shallow to reduce magnetic body forcesacting between the pole pieces 95v, 95v' and the magnetic return 92v.

In the MR mounting 20w of FIG. 17, a similar preferably nonmagneticspring 84w suspends the magnetic return 92w relative to pole pieces 95w,95w'. Flow from first chamber 28w into second chamber 30w causes a widergap and, therefore, less of a rheology change in the MR fluid 44w in thecontrollable passageway 42w. Likewise, flow from second chamber 30w tofirst chamber sees a enhanced MR effect because of the narrower gap,thereby providing increased damping relative to the compression stroke,i.e., the valve 18w provides "asymmetric" damping. Alternatively, thespring 84w could be manufactured from radially spaced segments ofelastomer bonded between the magnetic return 92w and divider 47w.

FIG. 18a-c illustrates another embodiment similar to that described withreference to FIGS. 15a-c. However, in this embodiment, the controllablepassageways 42x, 42x' are both formed between the outer ring 58x and thecenter portion 56x. The dimensional thickness tg1, tg2 of controllablepassageways 42x, 42x' are different, thereby providing a differentmagnetic reluctance for the magnetic circuit acting upon each. Forexample, the first magnetic circuit 40x acting upon the firstcontrollable passageway 42x has a first magnetic reluctance, while thesecond magnetic circuit 40x' acting on second controllable passageway42x' has a preferably higher reluctance. One-way check valves 34x, 34x'are interactive with each of the controllable passageways 42x, 42x', andsubstantially restrict flow of MR fluid in one direction through eachcontrollable passageway 42x, 42x', and allow flow in the oppositedirection.

Notably, check valve 34x allows flow in compression through passageway42x, while check valve 34x' allows flow through passageway 42x' inextension. Contrarily, check valve 34x cuts off flow of MR fluid throughfirst controllable passageway 42x in extension, and check valve 34x'cuts off flow through passageway 42x' in compression. Preferably,one-way check valves 34x, 34x' comprise butterfly-shaped flexures whichblock substantially all of each of the passageways 42x, 42x' on one endthereof. Passageways 42x, 42x' are formed by differing thickness annularsections formed on ring 58x which interact with the outer periphery ofthe center portion 56x. Segments 83x extend from the bottom to the topof valve body 32x. Segments 83x are preferably nonmagnetic and preventflow between the first controllable passageway 42x and the secondcontrollable passageway 42x' in the circumferential direction. Checkvalve 34x is preferably secured to valve body 32x by step on piston rod25x. Likewise, check valve 34x' is preferably secured to valve body 32xby fastener, welding, adhesive, or the like. The valve assembly 18xprovides "asymmetric", yet tunable damping in both directions of thedamper 20w. Notably, it should be recognized that this valve'sconfiguration could be used in a MR fluid mounting or in a stand alonecontrol valve.

FIG. 19a-b illustrates two positions of a valve assembly 18y which findsutility in linear-acting MR damper 20y. The valve assembly 18y includesan annular outer ring 58y which interacts with the center portion 56ywhich includes pole pieces 95y, 95y' to form the controllable passageway42y. The valve 18y includes a spring 84y, such as the multipleBelleville springs shown, which flexibly support the pole piece 95y'.Depending upon the direction of travel of the piston assembly 24y, thepole piece 95y is either in the upper position, as shown by FIG. 19b(ex. in compression) or in the lower position, as shown in FIG. 19b (ex.in extension). When the pole piece 95y' is positioned in the upperposition (FIG. 19a), the magnetic circuit 40y has high reluctance, andthus, a low force is produced in compression. This lower force isproduced because the magnetic circuit reluctance is high becausepreferably annular-shaped nonmagnetic spacer 73y is present within themagnetic circuit 40y (the weak magnetic strength indicated by thethinner dotted line).

However, when the piston is stroked in extension, the pole piece 95y'axially compresses spring 84y, which aligns the pole piece 95y' (whichis manufactured from a soft-magnetic material) with the center portion56y and, therefore, the magnetic short circuit is removed and themagnetic circuit 40y' exhibits lower reluctance, and, thus, higher forceis produced in extension. Preferably, a disc-like nonmagnetic retainer70y prevents the pole piece 95y' from moving too far. It should beunderstood that the motive force which urges the pole piece 95y' to movefrom the "upper" to the "lower" position is pressure acting upon theface of the pole piece 95y'. It also should also be recognized that themeans for providing "asymmetry" is a magnetic circuit reluctance whichis varied as a function of flow direction. The reluctance varies from a"high" value in the upper position to a "low" value in the lowerposition, and may provide many intermediate reluctance values dependingupon the pressure acting on the face of pole piece 95y'.

FIG. 20 illustrates another valve assembly 18z within a piston 24z oflinear-acting MR damper 20z. This embodiment includes dual coils 46z,46z' each generating a magnetic field which acts upon differentcontrollable passageways 42z, 42z'. One way valves 34z which takes theform of a ring-like sliding member with a triangular cross-sectionalarea operates to force flow through controllable passageway 42z incompression and force flow through controllable passageway 42z' inextension. Similar to the FIG. 12a embodiment, the current to coils 46z,46z' are independently adjustable and preferably receive a DC bias,which may be different. Further the reluctance of the magnetic circuits40z, 40z' may be different. Notably, during the compression stroke, flowis generally in through ingress 90z and out through the firstcontrollable passageway 42z, as the DC bias prevents any substantialflow through second controllable passageway 42z'. Check valve 34z is inintimate contact with upper intermediate ring 57z thereby closing offingress 90z'. Likewise, in extension, flow is in through ingress 90z'and out through second controllable passageway 42z'. Check valve 34z isin intimate contact with lower intermediate ring 57z' thereby closingoff ingress 90z. Welds secure outer ring 58z, intermediate rings 57z,57z', and center portion 56z together.

FIG. 21 illustrates another valve assembly 18u within the piston 24u inlinear-acting MR damper 20u. This embodiment includes a plurality ofcontrollable passageways 42u, 42u' and a single coil 46u. In compressionoperation, ball 94u of one-way check valve 34u closes off the pluralityof ingress ports 90u" and fluid flows in through first controllablepassageway 42u and out through egress 90u. Flow in egress 90u' isblocked off by flexure-type one-way check valve 34u'. In extension, theball 94u moves to the position shown in dotted lines and flow is inthrough ingress ports 90u" through second controllable passageway 42u'and out through egress 90u'. Flow through first controllable passageway42u is blocked by ball 94u. Flow through egress 90u is blocked byflexure-type one-way check valve 34u'. Preferably, the reluctance of themagnetic field acting on the first controllable passageway 42u and thesecond controllable passageway 42u' is different. This is preferablyaccomplished by making the dimension of the first controllablepassageway 42u smaller than the second controllable passageway 42u' suchthat damping force in extension is higher than in compression. Thievalve body 32u is comprised of annular ring 58u, center portion 56u, andend poles 57u, 57u'. The flexure discs 34u', 34u" are secured to ends57u, 57u' by nuts 59u, 59u'. Ring 58u, center portion 56u, and end poles57u, 57u' are secured together via welds or the like.

In summary, its should be recognized from the foregoing that the presentinvention is a controllable MR valve assembly which finds applicationalone, in MR dampers, or in MR mountings. The MR valve assembly istwo-way acting (designed to accommodate flow in two directions) andprovides for passively obtained damping "asymmetry", i.e., a higherdamping force in a first flow direction, and a lower damping force in asecond flow direction. Various means for providing the "asymmetrical"damping are described herein, such as: 1) providing one or more passivepassageways with a "one-way check valve" operative therewith which arelocated in parallel relationship to the controllable passageway, or 2)providing a "changeable flow gap" via a moveable wall portion in thecontrollable passageway, or 3) providing a "first controllablepassageway" for flow in a first direction and a "second controllablepassageway" for flow in a second direction, or 4) providing means forvarying the "magnetic reluctance" of the magnetic circuit as a functionof flow direction, such as by having a "high magnetic reluctancesection" which is toggled into, and out of, the magnetic circuit as afunction of flow direction.

While several embodiments including the preferred embodiment of thepresent invention have been described in detail, various modifications,alterations, changes, and adaptations to the aforementioned may be madewithout departing from the spirit and scope of the present inventiondefined in the appended claims. It is intended that all suchmodifications, alterations, and changes be considered part of thepresent invention.

We claim:
 1. A two-way controllable magnetorheological fluid valveassembly, comprising:(a) a valve body having at least a portion of amagnetic circuit contained therein which is capable of carrying amagnetic flux, (b) a controllable passageway adjacent to said valve bodyin a vicinity of said magnetic circuit, (c) a Magnetorheological fluidcontained in said controllable passageway, (d) a magnetic flux generatorfor generating a magnetic flux which is carried by said magnetic circuitand which is directed to act upon said magnetorheological fluid in saidcontrollable passageway to provide controllable rheology changes to saidmagnetorheological fluid in said controllable passageway therebyrestricting flow through said controllable passageway, and (e) a passivepassageway arranged in parallel relationship to said controllablepassageway, said passive passageway having a one-way check valvefluidically operative therewith so as to substantially restrict flow ina first flow direction and allow flow in a second flow direction, saidpassive passageway being situated with said magnetic circuit, yet adimension of said passive passageway is large enough relative to acomparable dimension of said controllable passageway such that saidmagnetorheological fluid passing through said passive passageway doesnot exhibit any significant rheology change.
 2. A two-way controllablevalve assembly, comprising:(a) a valve body having a high reluctancemagnetic circuit and a low reluctance magnetic circuit containedtherein, said high and low reluctance magnetic circuits capable ofcarrying a low and a high magnetic flux, respectively, (b) first andsecond controllable passageways adjacent to said valve body, (c) aMagnetorheological fluid contained in said first and second controllablepassageways, (d) a magnetic flux generator for generating said high andlow magnetic flux which are carried by said high and low reluctancemagnetic circuits and which are directed to act upon saidmagnetorheological fluid in said first and second controllablepassageways to provide controllable rheology changes therein, and (e) afirst one-way check valve operative with said first controllablepassageway substantially restricting flow in a first flow direction andallowing flow in a second flow direction, and (f) a second one-way checkvalve operative with said second controllable passageway substantiallyrestricting flow in said second flow direction and allowing flow in saidfirst flow direction.
 3. A two-way controllable valve assembly,comprising:(a) a valve body having at least a portion of a magneticcircuit contained therein which is capable of carrying a magnetic flux,(b) a controllable passageway adjacent to said valve body in a vicinityof said magnetic circuit, (c) a Magnetorheological fluid contained insaid controllable passageway, (d) a magnetic flux generator forgenerating a magnetic flux which is carried by said magnetic circuit andwhich is directed to act upon said magnetorheological fluid in saidcontrollable passageway to provide controllable rheology changes to saidmagnetorheological fluid ill said controllable passageway therebyrestricting flow through said controllable passageway, and (e) means forinterjecting a magnetic short into and out of said magnetic circuit as afunction of flow direction in said controllable passageway therebycausing a high magnetic circuit reluctance when said magnetic short isin said magnetic circuit, thus a lower damping force, and a low magneticreluctalnce when said magnetic short is out of said magnetic circuit,thus a higher damping force.